1. Field of the Invention
The present invention relates to a polypropylene resin composition. More particularly, it pertains to a polypropylene resin composition excellent in coating properties, peeling strength and elasticity.
2. Description of Related Arts
An automobile bumper has heretofore employed a composition of polypropyelen (PP) with ethylene/propylene rubber (EPR). Since polypropylene is extremely poor in coating properties because of its being devoid of a polar group in the molecular and thus chemically inactive, etching with trichloroethane or the like is indispensable in the case of applying coating to a bumper made of such a composition as mentioned above. In addition, it has heretofore been a general practice to perform etching treatment with trichloroethane as pretreatment in the case of applying coating to a polypropylene-based composite material, needless to repeat such a automobile bumper, for the purpose of developing a practically acceptable coating strength. (Refer to Surface Engineering Practice by Shosaku Yamamoto and Mikio Uchida, 31 (10), 440 (1984))
However, trichloroethane is one of the contributors to environmental destruction such as destruction of the ozone layer and therefore, should be excluded from the etching method using it.
As an alternative to trichloroethane, mention may be made of an aqueous alkali solution of a surfactant, which however has not been usable for applying coating to a polypropylene-based composite material typified by a bumper made thereof because of its extremely poor cleaning dissolving performance.
On the other hand, there is reported a method of improving coating properties by blending a polar substance with PP to form a composition, which is exemplified by a composition of PP resin with polyvinyl phenol (Japanese Patent Application Laid-Open No. 9941/1991) and a composition of PP resin with an ethylene/carboxylic acid compound copolymer (Japanese Patent Application Laid-Open No. 278862/1991). Nevertheless, any of the above-mentioned compounds has not a sufficient adhesiveness in the coating as a bumper material to be coated after cleaning with a water-based cleaning agent.
Under such circumstances, intensive research and investigation were concentrated by the present inventors into the development of a PP resin composition capable of being coated immediately after degreasing and suitable for recoating without pretreatment with a halogen-containing organic solvent such as trichloroethane as well as the elimination of the above-described problems.
As a result, it has been found by the present inventors that a composition of a specific compound that had theretofore been used as an electrifying agent with a modified polyolefin having a functional group introduced therein has excellent coating properties and the use of such composition can attain the object of improving coating properties. The present invention has been accomplished on the basis of the above-mentioned finding and information.